Branched polymer cross-linked graphene oxide adsorbent material

ABSTRACT

A graphene oxide adsorbent material for filtering contaminants from water is formed of graphene oxide plates cross-linked by branched polymer nanoparticles.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims the benefit of U.S. Provisional ApplicationSer. No. 62/966,247, filed Jan. 27, 2020.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with Government support under Federal Grant nos.EF-0830093 and DBI-1266252 awarded by the National Science Foundation.The Federal Government has certain rights to this invention.

BACKGROUND

Availability of clean water is an ongoing and growing global challenge,exacerbated by climate change, increasing population, and pollution. Tocounter this new threat, new materials and technologies for waterremediation have emerged. A variety of methods, including ion exchange,electrolysis, and sorption, have been applied to remove pollutants fromaquatic ecosystems. Among these methods, sorption is one of the mostpromising techniques for water remediation due to its outstandingcharacteristics, such as cost-effectiveness, eco-friendliness, and fastperformance.

BRIEF SUMMARY

The Summary is provided to introduce a selection of concepts that arefurther described below in the Detailed Description. This Summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

One aspect of the present disclosure provides an adsorbent material,comprising, consisting of, or consisting essentially of graphene oxideplates cross-linked by branched polymer nanoparticles.

Another aspect of the present disclosure provides a method of removingcontaminants from water using the disclosed adsorbent material.

DETAILED DESCRIPTION

The accompanying Figures are provided by way of illustration and not byway of limitation. The foregoing aspects and other features of thedisclosure are explained in the following description, taken inconnection with the accompanying example figures (also “FIG.”) relatingto one or more embodiments, in which:

FIG. 1 is a photograph of a graphene oxide adsorbent material inaccordance with one embodiment of the present disclosure;

FIG. 2 is a photograph of a graphene oxide adsorbent material duringsynthesis process, after mixing;

FIG. 3 is a photograph of the graphene oxide adsorbent material of FIG.2, after adding acetone;

FIG. 4 is a photograph showing a close-up image of the bubbles formingon the surface and throughout the sponge material after addition ofacetone as shown in FIG. 3, confirming a successful reaction; and

FIG. 5 shows a plot comparing adsorption capacity of activated carbon,unmodified sponge, and the described graphene oxide adsorbent material.

DETAILED DESCRIPTION

Branched polymer cross-linked graphene oxide adsorbent material isprovided. The described material can be used for water remediation, bothin small scale systems and large scale systems.

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to preferred embodimentsand specific language will be used to describe the same. It willnevertheless be understood that no limitation of the scope of thedisclosure is thereby intended, such alteration and furthermodifications of the disclosure as illustrated herein, beingcontemplated as would normally occur to one skilled in the art to whichthe disclosure relates.

Articles “a” and “an” are used herein to refer to one or to more thanone (i.e. at least one) of the grammatical object of the article. By wayof example, “an element” means at least one element and can include morethan one element.

“About” is used to provide flexibility to a numerical range endpoint byproviding that a given value may be “slightly above” or “slightly below”the endpoint without affecting the desired result.

The use herein of the terms “including,” “comprising,” or “having,” andvariations thereof, is meant to encompass the elements listed thereafterand equivalents thereof as well as additional elements. As used herein,“and/or” refers to and encompasses any and all possible combinations ofone or more of the associated listed items, as well as the lack ofcombinations where interpreted in the alternative (“or”).

As used herein, the transitional phrase “consisting essentially of” (andgrammatical variants) is to be interpreted as encompassing the recitedmaterials or steps “and those that do not materially affect the basicand novel characteristic(s)” of the claimed invention. Thus, the term“consisting essentially of” as used herein should not be interpreted asequivalent to “comprising.”

Moreover, the present disclosure also contemplates that in someembodiments, any feature or combination of features set forth herein canbe excluded or omitted. To illustrate, if the specification states thata complex comprises components A, B and C, it is specifically intendedthat any of A, B or C, or a combination thereof, can be omitted anddisclaimed singularly or in any combination.

Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. For example, if a concentration range isstated as 1% to 50%, it is intended that values such as 2% to 40%, 10%to 30%, or 1% to 3%, etc., are expressly enumerated in thisspecification. These are only examples of what is specifically intended,and all possible combinations of numerical values between and includingthe lowest value and the highest value enumerated are to be consideredto be expressly stated in this disclosure.

Unless otherwise defined, all technical terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this disclosure belongs.

The material disclosed herein is a water contaminant adsorbent material,comprising graphene oxide plates cross-linked by branched polymernanoparticles. Under the correct conditions, the branched polymercross-linked graphene oxide self-assembles into macroscopic sponge-likearchitectures.

FIG. 1 is a photograph of a graphene oxide adsorbent material inaccordance with one embodiment of the present disclosure. In particular,FIG. 1 is a microscope image of a graphene oxide adsorbent “sponge” witha width of several millimeters. To produce the disclosed adsorbentmaterials, single graphene oxide plates, which are suspended in water,are permanently cross-linked by branched amine polymers. This results ina macroscopic material several millimeters in diameter. The materialscan be further modified by facile reactions with ketone groups at theremaining amine surfaces. The resulting sponge-like structure has a lowfluid flow resistance and is highly water retentive.

According to various embodiments, synthesis can be optimized to minimizematerial waste and make synthesis as simple as possible in terms of thefeasible dilutions of components. In an example implementation, thefabrication process for graphene oxide adsorbent sponges includes thefollowing steps.

In step 1, the process includes preparing stock solutions of GrapheneOxide (GO, 0.2 g/L) and high molecular weight Branched Polyetheleneimine(bPEI, 1 g/L), both with pH adjusted to 7.0.

In step 2, the process includes combining the prepared solutions in aratio of 10:1 GO:bPEI.

In step 3, the process includes mixing the combination. The mixing canbe performed, ideally by vortexing or vigorous shaking (see e.g., FIG. 2described below).

In step 4, the process includes adjusting the pH of the mixedcombination to 5.5.

In step 5, the process includes adding acetone with weight approximatelyequal to the mass of bPEI used in synthesis (see e.g., FIGS. 3 and 4described below).

These five steps result in a “base” material.

FIGS. 2-4 are photographs illustrating the synthesis process. FIG. 2 isa photograph of a graphene oxide adsorbent material during synthesisprocess, after mixing (e.g., step 3); FIG. 3 is a photograph of thegraphene oxide adsorbent material of FIG. 2, after adding acetone (e.g.,step 5); and FIG. 4 is a photograph showing a close-up image of thebubbles forming on the surface and throughout the sponge material afteraddition of acetone as shown in FIG. 3, confirming a successfulreaction. As can be seen in FIG. 4, the formation of bubbles andmaterial rising to the surface indicates successful reaction with theketones.

In some implementations, the base graphene oxide adsorbent material canbe customized. For example, for customization, some fraction of acetonecan be replaced with other ketones containing the desired surfacegroups. The capping by the acetone (and/or other ketones) halts anyfurther cross-linking reaction, and allows the material to be storedlong term at neutral pH.

Indeed, after adding the acetone or acetone and other ketone(s) asdescribed in step 5, step 6 can be carried out by separating synthesizedmaterial from water and rinsing the material with clean water. Step 6may be carried out, for example, by decanting, simple filter paper, meshscreens, etc. The separated, rinsed material can then be collected andstored for future use. It should be understood that the remainingconcentrated material with associated water should not be allowed tofully dry.

The above strategy of ketone-capping the material allows for long termstorage and stability. Further, the ketones used in the above-describedsynthesis process may be removed and subsequently replaced with a ketoneof choice by lowering the pH below 5, washing, raising pH to 5.5, andreacting with any fresh ketone.

The mechanism of cross-linking is an epoxy reaction; bPEI amine groupsopen the epoxide rings present at the surface of graphene oxide and formcovalent bonds. The branched nature of bPEI allows this reaction withmultiple graphene oxide plates, thus cross-linking them permanently.Advantages of this mechanism over others include the covalent nature ofthe linking, and the lack of any chemical pre-processing of the grapheneoxide.

As can be seen, the primary amines in bPEI perform a ring opening epoxyreaction to covalently bind with the epoxide groups in the plane ofgraphene oxide. Functionalization for contaminant targeting happens at“leftover” primary amines on bPEI.

Customization of the sponge's surface chemistry by addition of differentketones allows one to target specific contaminants which may otherwisebe poorly removed by conventional means. Indeed, it is possible tofunctionalize the bPEI cross-linker within the structure instead ofhaving to functionalize the graphene oxide itself. Examples of materialsfor functionalization include any metal chelating agent that can beattached to an amine group. In some cases, a derivative of2-pyridinecarboxaldehyde thiosemicarbazone (2-PTSC) can be used forremoving Hg, 1,8-dihydroxyanthraquinone (DHAQ) can be used for removingPb, long chain organic compounds can be used to facilitate binding withoily molecules, and multi-valent charged molecules can be used forremoving ions (and even for ion exchange).

The disclosed adsorbent materials have several advantages overconventional filtration materials. First, they can have extremely highsurface area per mass due to their nanoscale structure, far greater thancommonly used activated charcoal and other filter materials. Alsodifferent from many other nanoparticle-based materials, their permanentcross linking also makes them large enough to settle out of solution intanks or to be incorporated in filtration cartridges. Further, thecombination of materials offers multiple modes of contaminant removalthrough physical and chemical processes. Such a wide range of mechanismsand capabilities are not offered by the most common current filtrationmethods. Moreover, additional functional groups present on the polymercross-linkers provide potential attachment structure for additionalligands for targeted contaminant removal. The combination of thesefactors can allow significant advantages over traditional filters suchas fiber filters or activated charcoal, such as the ability to remove afar wider range of contaminants, including typically challenging speciesfor filtration such as lead, antibiotics, and pesticides.

In some embodiments, the disclosed adsorbent materials also provideopportunities to attach ligands capable of selectively removing elementsof qualitative or scientific value from water. Ketone groupcustomization allows for the removal of contaminants or concentration ofvaluable resources not possible by traditional filters or adsorbents.Some non-limiting examples include heavy metals, nutrients, smallmolecule toxins, and radio nucleotides. These ketone groups are alsoeasily removed and replaced after use without destroying the frameworkmaterial, and refreshed. They may also be added to the material in anycombination, allowing for multi-functional customization.

Another advantage of the disclosed material is that the synthesisprocess can be achieved using a very low energy input, in contrast withconventional solutions, such as activated charcoal, which is thermallytreated. Further, the open structure easily allows water to flow throughin ambient conditions and is highly water retentive. This prevents theaccidental drying issues faced by activated carbon filters.

In summary, the disclosed material is a low energy cost, customizable,adsorbent material capable of removing a wide variety of components fromwater.

Another embodiment of the present disclosure provides a method oftreating water using the disclosed materials. As will be evident to aperson of skill in the art, the adsorbent material can be deployed in anumber of different ways. For example, it can be in the form ofcartridges for home use in whole-home or under sink filtration, or incountertop consumer filtration systems. In other embodiments, it can beused by industrial companies in order to efficiently purify theirhigh-volume wastewater streams in order to stay in environmental policycompliance. In another example, it may be used in large cartridges orsettling tanks in municipal water treatment as a way to removecontaminants not well removed by most current methods, includingdisinfection byproducts and many small molecules such as pesticides andantibiotics.

Prototype Example

As illustrated in FIGS. 1-4, a graphene oxide adsorbent material wasfabricated according to the synthesis method described above. X-RayDiffraction (XRD) testing of the material, even dried, confirms acompletely amorphous structure. This then confirms that thecross-linking of graphene oxide by bPEI successfully disrupted thestacked structure of the graphene oxide, also leaving voids between theplates for adsorption.

An adsorption benchmark test was carried out using methylene blue (MB)dye, a common standard in the industry. The capacity to adsorb this dyeand remove the dye from water was carried out for two materials: the“base” material herein (“Unmodified”, acetone-capped), and a customizedmaterial capped with 50% acetone, 50% pyruvic acid (Mod1). These werecompared with a range of values from peer-reviewed literature forcommercial activated carbon. The results are shown in FIG. 5. FIG. 5shows a plot comparing adsorption capacity of activated carbon,unmodified sponge, and the described graphene oxide adsorbent material.As reflected in the plot, the unmodified material matched thecommercial-grade activated carbon in adsorption capacity, while the Mod1material (capped with 50% acetone, 50% pyruvic acid) surpassed thiscapacity by approximately 50%. This is a clear demonstration that thematerial can also be customized to target specific contaminants forenhanced removal.

Although the subject matter has been described in language specific tostructural features and/or acts, it is to be understood that the subjectmatter defined in the appended claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed as examples of implementing theclaims and other equivalent features and acts are intended to be withinthe scope of the claims.

What is claimed is:
 1. An adsorbent material, comprising graphene oxideplates cross-linked by branched polymer nanoparticles.
 2. The adsorbentmaterial of claim 1, further comprising at least one functional group oncross-links of the branched polymer nanoparticles.
 3. The adsorbentmaterial of claim 2, wherein the at least one functional group comprisesa metal chelating agent that is attachable to an amine group.
 4. Theadsorbent material of claim 2, wherein the at least one functional groupcomprises 2-pyridinecarboxaldehyde thiosemicarbazone (2-PTSC) or aderivative thereof.
 5. The adsorbent material of claim 2, wherein the atleast one functional group comprises 1,8-dihydroxyanthraquinone (DHAQ).6. The adsorbent material of claim 2, wherein the at least onefunctional group comprises a long chain organic compound.
 7. Theadsorbent material of claim 2, wherein the at least one functional groupcomprises a multi-valent charged molecule.
 8. A method of removingcontaminants from water, comprising filtering the water through theadsorbent material of claim
 1. 9. A method of fabricating an adsorbentmaterial comprising: preparing stock solutions of Graphene Oxide (GO,0.2 g/L) and high molecular weight Branched Polyetheleneimine (bPEI, 1g/L), both with pH adjusted to 7.0; combining the prepared stocksolutions in a ratio of 10:1 GO:bPEI into a combined solution; mixingthe combined solution; adjusting the pH of the combined solution to 5.5after mixing the combined solution; adding at least one ketone to thecombined solution after adjusting the pH to 5.5 to form a synthesizedmaterial in water; and separating the synthesized material from thewater and rinsing the separated synthesized material with clean water.10. The method of claim 9, wherein mixing the combined solutioncomprises vortexing the combined solution.
 11. The method of claim 9,wherein mixing the combined solution comprises vigorous shaking of thecombined solution.
 12. The method of claim 9, wherein adding the atleast one ketone adds a combined weight of the at least one ketoneapproximately equal to the mass of the bPEI combined in the combinedsolution.
 13. The method of claim 9, wherein the at least one ketonecomprises acetone.
 14. The method of claim 9, wherein the at least oneketone comprises acetone and a second ketone.
 15. The method of claim 9,further comprising storing the separated synthesized material withassociated water for a neutral pH.
 16. The method of claim 9, whereinseparating the synthesized material from the water comprises decanting.17. The method of claim 9, wherein separating the synthesized materialfrom the water comprises using a filter paper.
 18. The method of claim9, wherein separating the synthesized material from the water comprisesusing a mesh screen.
 19. The method of claim 9, further comprising:removing one or more of the at least one ketone from the synthesizedmaterial; and replacing the removed one or more of the at least oneketone with a different ketone.
 20. The method of claim 19, wherein theremoving of the one or more of the at least one ketone and replacing theremoved one or more of the at least one ketone with a different ketonecomprises: lowering the pH of a solution with the synthesized materialbelow 5; washing the synthesized material; raising the pH of the washedsynthesized material to 5.5; and reacting with fresh ketone.